Could this be a clue of sorts? The image could hint at a linear progression, perhaps to leap higher and higher with the possibility to be sucked deeper and deeper in to the tubes. Height and depth could be the ideas conveyed here. Also, the number three may play a role. Obviously, there are three dimensions. But the first two tubes could also stand for the Nintendo DS family and Wii console - the current consoles and cornerstones of Nintendo's success - with the promise of the next hardware surpassing them. I believe that the ideas of progression and extension are quite obviously evident here. What do you come up with?
EDIT Here is the image within the context of the mail invite.
EDIT Reader Kevin noted that this image was already part of last year's invite and has kindly uploaded an image. He also asserts that it was used before then. I have to admit that I did not remember. But now, I think we can safely assume that the image contains no hidden meaning with regard to Nintendo's next home console.